"fons omnis sanctitatis": the roughly 7th/8th-century Liber mozarabicus sacramentorum. Unfortunately, I haven't yet turned it up there: not by searching, and not by checking the indices, e.g. under fon* and sanctit*. A search of the 2002 edition of the Library of Latin Texts (e.g. omn* sanctit*, which occurred 5 times; as well as variants; but examine more closely the many more hits on fon* /5 omn* /5 sanct*; omn* /1 sanctit*; and so forth) also failed to turn up anything relevant, the sole exception being Lumen gentium 47 ("the one and undivided Trinity, which in Christ and through Christ is the source and origin of all holiness [(omnis sanctitatis fons et origo)]").

"Spiritus tui rore santifica" ("sanctify with the dew of your Holy Spirit"): Missale Gothicum no. 271, c. 700 (where the phrase appears to be actually "spiritus sancti tui rore perfundas" ("[We ask that you bless this sacrifice with your benediction and] bedew [it] with the dew of your Holy Spirit[, so that it may be for all a lawful Eucharist]"); but check also CCSL 159D (2005)).